We have developed a cytotoxicity system for the assay of cell-mediated immunity (CMI) against hepatitis B virus (HBV) using two established human hepatoma cell lines (PLC/PRF/5 and Hep 3B) as target cells. These cells produce hepatitis B surface antigen (HBsAg) and express liver-specific protein (LSP) and HBsAg on their surface. Our preliminary studies, along with other reports, have indicated that CMI plays a role in the diverse sequelae of HBV infection. In the follow-up studies we plan to further characterize the involvement of the immune system in the pathogenesis of viral hepatitis B, especially as it relates to the carrier state. (1) We will assess the cytotoxic activity of lymphocytes obtained from patients with acute viral hepatitis (AVH), chronic active hepatitis involved and will examine the effect of interferon on noncytotoxic cells. Because the two HBsAg-secreting cell lines differ in their HLA types, the effect of the major histocompatability complex antigen(s) involved in the cytotoxic reaction will be ascertained. (2) We have found that the culture supernatant of lymphocytes from HBV carriers and from HBsAg vaccine nonresponders can suppress the cytotoxic response of lymphocytes from HBV convalescent patients against the PLC/PRF/5 cell line. We will isolate and characterize this suppressor factor. As an adjunct to a hepatitis B vaccine study soon to be initiated in normal and immunosuppressed volunteers, we will detrmine whether suppressor factor is present before inoculation of viral antigen and whether its presence serves as a prognostic marker of the eventual development of chronic liver disease. (3) We will examine the role of helper/inducer T cells in modulating immunoglobulin production during acute and chronic hepatitis.